In general terms, medical valving devices often act as a sealed port that may be repeatedly accessed to non-invasively inject fluid into (or withdraw fluid from) a patient's vasculature. Consequently, a medical valve permits the patient's vasculature to be freely accessed without requiring such patient's skin be repeatedly pierced by a needle.
Medical personnel insert a syringe into the proximal port of a properly secured medical valve to inject fluid into (or withdraw fluid from) a patient. Once inserted, the syringe may freely inject or withdraw fluid to and from the patient. Problems arise, however, when the syringe is withdrawn from many different types of prior art valves. Specifically, a back pressure (i.e., a proximally directed pressure) produced by the withdrawing syringe undesirably can cause blood to be drawn proximally into a catheter attached to the valve, or into the valve itself. In addition to coagulating and impeding the mechanical operation of the valve, blood in the catheter or valve also compromises sterility.